Process for conserving quinolic compounds in an organic extractant copper recovery system

ABSTRACT

Improvements are disclosed for a process of the type in which copper is produced by contacting an aqueous copper solution with a quinolic compound in an organic solvent to result in the precipitation and recovery of copper metal. In this type of process, the organic phase containing the extractant is separated from the copper depleted raffinate and the quinonic compound produced as a byproduct during copper precipitation may be reduced and used again for precipitating more metal salt. 
     A two step reduction of copper is disclosed. In a first step, cupric copper is reduced to cuprous copper and in the second step, cuprous copper is reduced to copper metal. 
     The inclusion of selected concentrations of chloride ions in the copper solution is disclosed to increase the rate at which copper is precipitated. 
     The in-situ conversion of quinolic compound contained in the raffinate by oxidation to the quinonic compound is also disclosed to reduce extractant losses in the aqueous phase. 
     A solvent system in which the percentage of aromatic solvent in a mixed organic solvent system is increased is also disclosed to increase the rate of reduction of copper metal.

BACKGROUND OF THE INVENTION

This invention relates to improvements in the extraction of copper fromsolutions by reduction with anthraquinols dissolved in a waterimmiscible solvent.

U.S. Pat. No. 3,820,979 to J. Manassen, entitled Process for theProduction of Metals, the disclosure of which is herein incorporated byreference, discloses a process for the production of copper, silver, andmercury from aqueous solutions containing these values. In the processof that patent, a quinolic compound (anthraquinol), which is dissolvedin a water immiscible organic solvent, contacts an aqueous solutioncontaining metal values of interest, such as copper ions, in either thecupric or cuprous state, to reduce the metal ions and to produce ametallic powder. After this reduction, the metallic precipitate isseparated; the organic and aqueous phases are separated; and, ifdesired, the quinolic compound, which is oxidized during the process toa quinonic compound (anthraquinone), is regenerated by reduction andused for treating further batches of aqueous metallic salt solutions.

Especially advantageous reducing agents are anthraquinols, which, duringthe reduction of the metals are oxidized to anthraquinones. Particularlysuitable anthraquinols are 2-methyl-anthraquinol, 2-ethyl-anthraquinol,2-propylanthraquinol, 2-isopropyl anthraquinol, 2-t-butyl anthraquinol,and 2-amyl-anthraquinol. Tetrahydroanthraquinols and 2-substitutedtetrahydroanthraquinols can also be used. The oxidized form of thesecompounds (anthraquinones) can be easily produced by condensation of asuitably substituted diene and napthaquinone, according to the procedureof Alan et al., Organic Synthesis 22,37 (1947). The quinol canthereafter be made by hydrogenation.

An important consideration in the choice of the particular anthraquinolto be employed is its solubility in the organic solvent system used.Preferred solvent systems suitable for the quinol and for the quinoneproduced during the process are combinations of nonpolar and polarsolvents. It is known that in order to minimize losses due to theevaporation of the organic solvent, nonpolar solvents such as alkyltoluenes, alkyl naphthalenes, or diphenyls are advantageously resortedto. Polar solvents, such as octanol and ethyl hexanol ordiisobutylketone are preferred. Esters such as dialkyl phthalates,diaryl phthalates, alkyl benzoates, benzyl acetates, ethyl heptanoatesand cyclohexanol acetates or propionates can be used as such or incombination with another organic solvent.

The Manassen patent also teaches that it is possible to reduce andprecipitate a large part of the reducible metals contained in thesolution by employing an excess of the reducing agent. In addition, itis taught to be advantageous to effect the process in two or morestages, using a suitable quantity of fresh organic solution in eachstage.

The Manassen patent, however, does not deal with many of the problemsthat would be encountered in practicing the process on a commercialscale. Specifically, the patent does not address itself to methods ofoptimizing the rate of precipitation of the metals of interest nor toconserving the organic extractant employed so as to provide anefficient, continuous process.

SUMMARY OF THE INVENTION

In accordance with the invention, it has been discovered that, in acopper recovery process of the type described, the reduced quinoliccompound (quinol), as a general phenomenon, is much more soluble inwater than is the oxidized quinonic compound (quinone). Because of thishigh solubility, the process is characterized by significant losses ofthe quinolic reductant through the copper depleated raffinate. Toprevent these losses, it has been discovered that water soluble quinoliccompounds may be recovered by oxidizing the, in-situ, to thecorresponding quinonic compound. In this regard, the aqueous phase leftover after the copper reduction is complete has been found to containupwards of 600 parts per million quinolic compounds before oxidation.However, after oxidation, the organic extractant concentration in theaqueous phase is on the order of 1 to 10 parts per million.

In accordance with another important aspect of the present invention, ithas been discovered that in such a process, the rate of reduction andprecipitation of copper increases as the pH of the copper containingsolution is increased.

It has been also discovered that when the percentage of aromatic solventin a mixed organic solvent system carrying the organic extractant isincreased over that taught in the prior art, the rate of reduction ofcopper to metal is increased.

These and other discoveries disclosed herein permit a process to bedesigned which significantly increases the rate of copper production andhas important economic advantages.

Accordingly, it is an object of the invention to increase the rate ofcopper precipitation in the known quinolic extraction reaction.

Another object of the invention is to provide a process for recoveringcopper metal from copper containing aqueous solutions which optimizesthe rate of copper precipitation and minimizes organic extractantlosses.

Another object of the invention is to conserve quinolic extractant in asystem for reducing copper of the type described by oxidizing quinoldissolved in the raffinate to the corresponding insoluble quinone,recovering the quinone, and reducing the quinone for further use in thesystem.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a diagram illustrating a prior art process for producingcopper metal by reducing copper ions with a quinolic compound;

FIG. 2 is a diagram illustrating several improvements of the processillustrated in FIG. 1; and

FIG. 3 is a diagram further illustrating various improvements of theprocess illustrated in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In order to facilitate understanding of the present invention, adescription of the prior art follows. In the prior art processes, asillustrated in FIG. 1, a pregnant solution 10 which may be an aqueousammoniacal leach liquor containing cupric ions is contacted with aquinolic compound 12 such as an anthraquinol. The aqueous phase 10 andthe organic phase 12 are mixed in a mixer 14 to effect reduction of thecupric copper to copper metal. The quinolic compound (anthraquinol) isoxidized to a quinonic compound (anthraquinone). The three phasesrepresented by stream 16 are sent to a filter and settler 18 where theyare separated into the three phases, that is, organic phase 20containing the quinonic compound, the aqueous phase 22, and the coppermetal 24.

The economics of a commercially successful system of the type disclosedrequires a rapid and complete removal of copper from solution andminimal losses of organic extractant in the raffinate. In the prior artprocess illustrated in FIG. 1, these two goals conflict because the useof an excess of the quinolic reducing agent 12, (the most expensivecomponent of the organic phase) to achieve complete and rapid removal ofcopper or other metals results in significant amounts of the quinolicreducing agent remaining dissolved in the raffinate 22. In this regard,it has been discovered that when ammoniacal solutions are treated torecover copper values, the reduction of cupric ions to cuprous ions byquinolic reducing agents is much faster than the reduction of cuprousions to copper metal using these reagents. The cupric ions to cuprousion reaction has been observed to take place quantitatively in less thanabout 5 seconds if the two phases are thoroughly mixed. On the otherhand, under optimum conditions, the reaction of cuprous ions to coppermetal takes place in about 2 to about 30 minutes.

When the organic and aqueous phases are thoroughly mixed in a singlevessel 14, the presence of excess quinolic reducing agent 12 acceleratesthe rate of copper reduction, but from a practical commercial point ofview, any more than a small excess of the reducing agent circulating inthe process stream 22 creates problems of separation and reagent losswhich are unacceptable. Furthermore, it is impractical to operate thesystem using a countercurrent flow of organic and aqueous phases becauseof the high cost associated with achieving a separation for a threephase system after each mixer stage.

In the preferred embodiment of the present invention, a two stagereduction system, as is shown in FIG. 2, is employed which combines arapid reduction of ammoniacal cupric solution, represented by stream 10,to form a stable, ammoniacal cuprous solution, represented by stream 26using minimal quantities of anthraquinol introduction through stream 28in a first stage. The reduction of the cuprous ions to copper metal isaccelerated by excess reducing agent represented by stream 32 in asecond stage. Accordingly, by using this two stage reduction scheme, animproved system for the recovery of copper can be designed. In the twostage system, as is shown in FIG. 2, only one three-phase separationneed be effected. Each stage 11 and 13 can include one or severalconcurrent mixers and can end in a phase separation step.

In the first stage 11, an ammoniacal cupric feed stream 10 is mixed withan appropriate amount of a quinolic reducing agent 28, which has beenalready partially used in second stage 13. Utilizing the appropriateamount of quinolic agent in mixer 34 results in formation of a stable(in the absence of oxygen) cuprous complex and in the oxidation of thequinol to a quinone.

Since no solid copper is formed in mixer 34, a conventionalaqueous-organic phase separation may be carried out in separator 39.Because of the aqueous-organic density difference and the need forrelatively minimal mixing, this separation can be effected rapidly andinexpensively by conventional techniques. The spent organic phaseexiting from the first stage 11 through stream 38 can then be cycled toa hydrogenator 40 for the regeneration and recycle. In the hydrogenator,the quinones are converted to quinols by reaction with hydrogen inaccordance with known procedures. The aqueous phase from the first stageis sent through stream 26 to the second stage 13 where it is contactedin mixer 42 with fresh quinol solution received via stream 32 from thehydrogenator 40. This stage, the slow step in a copper reductionprocess, is accelerated by the use of a quinol solution which contains astoichiometric excess, preferably twice as much, quinol as is necessaryto reduce the cuprous ion in solution to copper. By utilizing the twostages, the overall reaction rate of Cu⁺ ⁺→ CU⁰ is greatly accelerated.

In the second stage 13, the three phase slurry is delivered throughstream 44 to a phase separation stage 46 to be separated into coppermetal 30, aqueous phase 48, and organic phase 28. After being separatedfrom the aqueous phase in stage 46, the organic phase 28 containing thepartially spent quinol can then be directed to the first stage 11, wherethe balance of the quinol is consumed and where an excess is notrequired. The copper metal leaves the system for further processingthrough stream 30 and the raffinate may be treated as disclosed below.

Simplified chemical reactions for the process described above appearbelow:

    __________________________________________________________________________    IN CUPRIC REDUCTION STAGE 34                                                   ##STR1##                                                                     IN CUPROUS REDUCTION STAGE 42                                                  ##STR2##                                                                     IN THE HYDROGENATOR 40                                                         ##STR3##                                                                     __________________________________________________________________________

semiquinones, such as compounds have the structural formula: ##STR4##are believed to also take part in the reactions.

The two stage reduction of cupric ions is further illustrated by thefollowing non-limiting example.

EXAMPLE I

An aqueous, cupric ion containing solution was prepared by adding 19.65g of CuSO₄ .5H₂ O, 17.0 g of NH₃, and 36.0 g of (NH₄)₂ SO₄ in enoughwater to make 1 liter of solution. 21.3 g of 2-ethyl-anthraquinol weredissolved in enough mixed solvent comprising 70% xylene (nonpolar) and30% 2-ethyl-hexanol (polar) to produce 1 liter of solution. At 50° C.and under an inert atmosphere, 100 ml of the aqueous solution wereplaced in a 500 ml reactor vessel fitted with baffles and a 5 cm marinepropeller rotatable at 2000 rpm. An amount of the mixed solventcontaining the quinol prepared as disclosed above containing thestoichiometric amount of 2-ethylanthraquinol necessary to reduce all Cu⁺⁺ to Cu⁺ was then added to the vessel and the propeller was energized.When the Cu⁺ ⁺ was reduced to Cu⁺ the mixing was stopped and the spentorganic phase removed. A two fold excess of quinol was added to thereaction vessel and the propeller energized. The results of two runsutilizing this procedure are set forth below:

    ______________________________________                                        TIME (MIN.)      PPM Cu.sup.+.sup.+in Aqueous Phase                                          No. 1     No. 2                                                ______________________________________                                        0                5000        5000                                             1                --           292                                             2                23.7        4.83                                             ______________________________________                                    

As can be seen from these data, essentially quantitative reduction ofCu⁺ to Cu^(o) was achieved in a very short time. The partially spentorganic phase can now be used to reduce Cu⁺ ⁺ to Cu⁺.

According to another aspect of the invention, it has been discoveredthat the pH of the aqueous phase, i.e., the pH of phase 10 containingthe copper ions, influences the rate of copper reduction. In general,the higher the pH, the faster the reaction rate. A study of reactionrates versus pH in the alkaline range indicates that, in general, therate increases as pH increases. Similar behavior has been observed inthe acid range. However, extrapolation of pH-reaction rate curves overthe entire pH range is not feasible. This latter behavior is believed tobe a direct result of the different copper species present in ammoniacaland acid solutions.

During the reduction of copper, hydrogen ions are liberated when thequinonic compounds are formed and hence, the pH is lowered as thereduction proceeds. In view of this phenomenon, in accordance with theteaching of this invention, the ideal process should employ coppersolutions having a pH on the order of 9.5 or higher, e.g., fairlyconcentrated ammoniacal solutions, thereby decreasing the time requiredto achieve a suitable amount of copper reduction. The preferred pH valuerange is from about 9.5 to about 11.0. Obviously, this discovery may beutilized to advantage in conventional anthraquinol copper extractionprocesses such as those set forth in U.S. Pat. No. 3,820,979.

The preferred mode for practicing the invention utilizes chloride ionsto accelerate the reduction of copper ions. In this regard, U.S. Pat.application Ser. No. 720,415 filed on even date herewith, entitledProcess for Increasing the Rate of Copper Metal Production in a QuinolicExtraction System by John N. Gerlach, the teachings of which areincorporated herein by reference, is directed to the discovery that,depending on the concentration and the pH of the copper solution, thepresence of chloride ion in the copper containing aqueous solution canaccelerate, decelerate, or even prevent the reduction of copper to metalby quinols. In the acid range, low chloride concentrations have beenfound to accelerate the reduction process; whereas, high chlorideconcentrations slow or even stop the process. In the basic range, i.e.,pH above about 7, any concentration of chloride in the aqueous copperbearing liquor increases the reaction rate. Low concentrations ofbromide ion (Br⁻) and thiocyanate ion (SCN⁻) also increase the reactionrate and may be used in this modification of the process. Accordingly,it is apparent that a significant impact on the economics of the processcan be made by the inclusion of appropriate amounts of chloride ions,bromide ions, thiocyanate ions and mixtures thereof. The followingexamples illustrate the principle.

EXAMPLE II

Four ammoniacal copper solutions were subjected to batch treatment with2-ethyl-anthraquinol dissolved in a mixed solvent comprising 62.5%xylene and 37.5% 2-ethylhexanol at 40° C. At regular intervals, aliquotsof the solutions were extracted and analyzed for the presence of solublecopper (Cu⁺ ⁺ and Cu⁺). The concentration of Cu⁺ in the solutions andthe concentration of Cl⁻ are indicated below.

                  TABLE I                                                         ______________________________________                                        ALKALINE SOLUTIONS WITH AND WITHOUT CHLORIDE                                  ______________________________________                                        Tests    1         2         3       4                                        ______________________________________                                        M[Cl.sup.-]                                                                            0         0         0.015   1                                        M[Cu.sup.+]                                                                            0.079     0.077     0.077   0.079                                    ______________________________________                                                   1       2        3        4                                        Time in min. ppM Cu.sup.+.sup.+remaining in solution                          ______________________________________                                         5           --        3750     340    --                                     10           1472      1880     20     2                                      20           417        185      1     --                                     30            50         4      --     --                                     ______________________________________                                    

As can be seen from Table I by comparison of the results of the tests onsolutions 3 and 4 with those of solutions 1 and 2, the inclusion of Cl⁻significantly increases the rate at which copper is extracted from thesolution. Further, the acceleration is substantial at chlorideconcentrations as low as 0.015M and does not decrease as the molarity israised.

EXAMPLE III

Four acidic copper solutions were subjected to treatment with2-ethyl-anthraquinol dissolved in a mixed solvent comprising 62.5%xylene and 37.5% 2-ethylhexanol. The data in Table II set forth below isconsistent with Example 1, and clearly shows that the inclusion of smallconcentrations of chloride ion can significantly increase the reactionrate. Chloride ion concentrations of 0.8 M result in a substantialreduction in the rate of the reaction Cu⁺ ⁺ → Cu^(o) ; higherconcentrations completely stop the reaction.

                  TABLE II                                                        ______________________________________                                        ACIDIC SOLUTIONS WITH AND WITHOUT CHLORIDE                                    ______________________________________                                                  1       2        3     4     5                                      M[Cl.sup.-]                                                                             0       0.0008   0.08  0.8   0.8                                    M [Cu.sup.+.sup.+]                                                                      0.08    0.08     0.08  0.08  0.08                                   ______________________________________                                        Time (min.)   ppM Cu remaining in solution                                    ______________________________________                                        10      2300      370      560   5000  5000                                   20      900       1.2      --    4600  4800                                   30      250       1.0      5.2   4250  4800                                   ______________________________________                                    

A probable explanation for this phenomenon is that chloride ions canform a weak CuCl⁺ complex which is easily reduced to CuCl and thenfurther reduced to metal. At high chloride ion concentrations, thereaction only goes to the cuprous state, Cu⁺ ⁺→Cu⁺. The cuprous ionwhich is normally unstable in acidic aqueous solutions is apparentlystabilized as CuCl₂ ⁻, CuCl₃ ⁻², or CuCl₄ ⁻³ and as a result, cannot bereduced to the metallic state by anthraquinols.

Three examples were also performed to test the affect of Br⁻ ion andSCN⁻ ion on copper extraction rates. The results of these tests appearbelow. In each of these tests T=40° C. and the organic solvent comprised60% xylene and 40% 2-ethylhexanol.

    ______________________________________                                        EXAMPLE A                                                                     M[Br.sup.-]         0.00079                                                   M[Cu.sup.+.sup.+]   0.079                                                     ______________________________________                                        Time (Min.)   ppM Cu.sup.+ remaining in solution                              ______________________________________                                        2             890                                                             5             35                                                              ______________________________________                                        EXAMPLE B                                                                     M[SCN.sup.-]        0.00106                                                   M[Cu.sup.+.sup.+]   0.079                                                     ______________________________________                                        Time (Min.)   ppM Cu.sup.+ remaining in solution                              ______________________________________                                        2             8                                                               ______________________________________                                        EXAMPLE C                                                                     M[SCN.sup.-]        0.00086                                                   M[Cu.sup.+.sup.+]   0.079                                                     ______________________________________                                        Time (Min.)   ppM Cu.sup.+ remaining in solution                              ______________________________________                                        1             740                                                             2              11                                                             ______________________________________                                    

Chloride concentrations between 0.1 and 0.001 M have been observed toaccelerate copper reduction in both acidic and basic solutions relativeto identical solutions containing no chloride. In ammoniacal solutions,both low and high chloride concentrations increase the reaction rate.Accordingly, economic considerations will dictate the amount of chlorideion to be added to the copper solution. At present, in ammoniacalsolutions, a concentration of between about 0.001 M and 0.5 M ispreferred. Of course, chloride ion may be included in copper solutionsto be treated by extraction processes other than the two-stage processdisclosed herein. Similar effects would be observed by the use ofbetween 0.1 and 0.001 M concentrations of bromide ions or thiocynateions. Specifically this discovery of selected ion activity may be usedto advantage in the conventional copper recovery processes set forth inU.S. Pat. No. 3,820,979.

As stated above, the preferred prior art solvents for the quinoliccompounds used as reducing agents in the process consist of mutuallymiscible combinations of nonpolar solvents such as variously substitutedbenzenes and naphthalenes, and polar solvents such as alcohols, ketones,and esters. The quinones are dissolved primarily in the nonpolarsolvent, and the quinols are dissolved in the polar solvent.

According to another aspect of the invention, it has been discoveredthat the percent concentration of the nonpolar and polar solvents can bevaried to increase the reaction rate. Specifically, when the amount ofpolar solvent is decreased and nonpolar solvent is substituted therefor,unexpectedly, the reduction of dissolved copper to metal is increased.The following examples illustrate this principle.

EXAMPLE IV

Two ammoniacal copper solutions were prepared, each of which contained3,000 ppm aqueous copper. A first water immiscible solvent was preparedby adding 20 ml of the nonpolar solvent xylene and 80 ml of the polarsolvent diisobutylketone to form 100 ml of a 20% xylene solution. Asecond mixed solvent was prepared by adding 50 ml xylene to 50 ml ofdiisobutylketone to produce a 50% xylene mixed solvent. 14.8 grams of2-ethylanthraquinol were dissolved in each organic solution. The firstsolution was added to an aqueous copper solution and agitated. Thesecond solution was added to an identical aqueous copper solution andagitated. The rate of copper precipitation, as indirectly measured bythe ppm aqueous copper remaining in solution at various times during thereduction, is set forth in Table III below.

                  TABLE III                                                       ______________________________________                                        ______________________________________                                               20% xylene solution                                                                         50% xylene solution                                      Time (Min.)                                                                            ppm Cu remaining in solution                                         ______________________________________                                        0        3000            3000                                                 5        2675            1710                                                 10       2070             540                                                 15       1432             74                                                  ______________________________________                                    

As can be seen from these data, as the percentage of the nonpolarsolvent was increased from 20% to 50%, the rate of copper precipitationwas significantly increased.

EXAMPLE V

A. The procedure of Example IV was repeated except that 2-ethylhexanolwas substituted for the diisobutylketone, the aqueous solution contained5100 parts per million copper instead of 3000, and the two mixedsolvents prepared consisted of, respectively, 50% xylene and 60% xylene.The results of the rate of copper precipitation in these two systems areindicated in Table IV below.

                  TABLE IV                                                        ______________________________________                                               50% xylene solution                                                                         60% xylene solution                                      Time (Min.)                                                                            ppm Cu remaining in solution                                         ______________________________________                                         0       5100            5100                                                 10       2850            1472                                                 20       1340             417                                                 30        500             50                                                  ______________________________________                                    

B. The procedure of Example 5A was repeated with the aqueous solutioncontaining 5000 parts per million copper and the two solvents containing60% and 70% xylene respectively. Results are indicated in Table V below.

                  TABLE V                                                         ______________________________________                                               60% xylene solution                                                                         70% xylene solution                                      Time (Min.)                                                                            ppm Cu remaining in solution                                         ______________________________________                                        0        5000            5000                                                 2        2000            1062                                                 5         578              5                                                  10         4               1                                                  T = 50° C  pH = 9.8                                                    Ammoniacal copper solution                                                    slight excess of 2-ethylanthraquinol                                          ______________________________________                                    

As can be seen from the above data, even a relatively modest increase of10% xylene can significantly increase the rate of copper precipitation.In accordance with the invention, it is contemplated that the maximumamount of nonpolar solvent should be used in the mixed solvent, whichamount will be dependent upon the solubility of the particularanthraquinol/anthraquinone used, the concentration used, and thetemperature selected for the extraction. Non limiting examples of otheruseful nonpolar organic solvents include toluene, naphthalenes, andvarious other lower alkyl substituted benzenes. Non limiting examples oforganic polar solvents include alcohols, ketones, and esters. Of course,as will be appreciated by those skilled in the art, this discovery willfind utility in conventional anthraquinol copper recovery processes aswell as in the two step process as disclosed herein.

In accordance with the present invention, it has been discovered thatthe various quinols used in this process are much more soluble in waterthan their corresponding quinones. This water solubility variation isespecially pronounced for ammoniacal solutions where a water solubleammonium salt exists in equilibrium with the quinols, i.e.,

    H.sub.2 AQ+ 2NH.sub.3 ⃡ AQ.sup.= + 2 NH.sub.4.sup.+,

where AQ is the quinone moiety. In concentrated ammonia solutions, thequinols useful in this process are in fact completely miscible in water.Since, as indicated above, a practical commercial system requires both arapid and complete removal of copper from solution and a low loss of theorganic phase in the raffinate, it would be highly desirable to minimizelosses of the organic phase. In this regard, the preferred mode ofpracticing the two stage reaction process disclosed above includesoxidizing the quinol dissolved in the raffinate by bubbling an oxidizinggas therethrough. By utilizing this step, quinol losses through theraffinate exiting from separator 46 through stream 48 can besubstantially reduced. Air can be used with success in this process.Since quinones are much more insoluble in water under all conditionsthan are the corresponding quinols, the quinones form a precipitatewhich can be removed by filtration or extracted by a suitable organicsolvent. The quinone produced in oxidation reactor 50 (FIG. 2) is passedthrough stream 52 to eventially be reduced to quinol in hydrogenator 40.This treatment results in aqueous anthraquinone concentrations on theorder of 1 to 10 ppm versus 660 ppm before oxidation. The followingexample illustrates this principle.

EXAMPLE VI

A 10% ammonia solution of copper sulfate was contacted with an excess of2-t-butyl anthraquinol in an organic solvent consisting of 40%2-ethylhexanol and 60% xylene. After mixing 5 minutes, copper metal wasremoved by filtration and the organic and aqueous phases were separated.Before bubbling air through the aqueous raffinate, 600 ppm of 2-t-butylanthraquinol was present. After bubbling air through the raffinate toform insoluble 2-t-butyl anthraquinone, only 3 ppm of 2-t-butylanthraquinol remained.

It should be noted that the oxidation of the quinol which wouldotherwise be lost in the aqueous raffinate may take place either beforeor after the organic and aqueous phases are separated in stage 46, butin any case, of course, should not be effected prior to separation ofcopper from the liquid phases. While bubbling oxygen through theraffinate is a preferred method of oxidizing the quinol, those skilledin the art will appreciate that other oxidizing gases, such as chlorinegas, may be substituted for oxygen, and indeed, that solutions ofoxidizing agents such as ferric or hypochlorite ions may be added torecover the selected organic extractant in the oxidized form. Of course,this quinol recovery procedure may be used in a conventional quinolextraction copper recovery process of the type set forth in theaforementioned U.S. Pat. No. 3,820,979. In fact, the excesses, typically10 to 15%, of quinolic extractant used in such processes renders theadvantage achievable by this procedure particularly significant.

The foregoing principles and discoveries may be combined as desired toprovide an efficient commercial process for reducing copper containingsolutions to pure copper metal. FIG. 2 illustrates one embodiment of asystem designed for utilizing such a process. Obviously, those skilledin the art will be able to make modifications without departing from thescope of the instant invention.

In FIG. 2, an ammoniacal solution 10 of cupric ions which may beobtained by a variety of processes is added to a reactor 34 togetherwith a partially reduced portion of an anthraquinol 28 dissolved in anorganic solvent. If desired, the ammoniacal cupric solution 10 cancontain chloride, bromide or thiocyanate ions, e.g., 0.01 M. The ammoniaacts as a buffer to stabilize the pH of solution 10 which, optimallyshould be from about 9.5 to about 11. The organic solvent in which thepartially spent anthraquinol 28 is dissolved may contain both nonpolarsolvent and a polar solvent, and preferably, in order to increase thereaction rate, it will contain greater than about 50% of the nonpolarsolvent in accordance with the principals set forth above. Preferablythe mixed solvent will contain between 60-80 wt.% of the nonpolarsolvent. In reaction vessel 34, within 5 seconds, the Cu⁺ ⁺ is reducedto Cu⁺ which is stabilized in the ammoniacal solution by the formationof the cuprous amine complex: Cu(NH₃)₄ ⁺. Since this chemical changetakes place very rapidly, vessel 34 may be relatively small and thuswill be characterized by a low cost. To assure rapid reaction, it isessential that the organic and aqueous phases be intimately mixed toform a fine dispersion.

After reaction in vessel 34, the aqueous and organic solutions exitthrough stream 14 to a settler 39 where the aqueous solution containingCu⁺ ions and small amounts of dissolved anthraquinol are separated. Theorganic phase containing the anthraquinone is delivered to ahydrogenator 40 containing a catalyst such as Raney nickel, platinum,palladium or the like for reducing anthraquinone, in situ, toanthraquinol. The output 32 of the hydrogenator 40 and the ammoniacalcuprous solution passing in stream 26 from the settler 39 are mixedtogether in a reaction vessel 42 (second stage) and are agitated for asufficient amount of time to reduce substantially all the cuprous ion tocopper metal. The metal precipitates as a powder but will contain silverand mercury if either of these are present in the original ammoniacalcuprous solution. The copper powder may thereafter be separated as 30from the two-phase aqueous system by filtration, and melted or otherwiserefined as desired.

The high concentration of the anthraquinol in reactor 42 optimizes therate of reduction of cuprous ion to copper metal, which as indicatedabove, is the slow step in the two stage reduction. It should be notedthat only a slight stoichiometric excess of the total anthraquinolneeded for both stages need be circulated in the system as quinoliccompound from hydrogenator 40 because the quinolic compound firstcontacts a copper solution in reactor 42 which has already been reducedto Cu⁺. Thus, in reactor 42, more than twice the total stoichiometricamount of anthraquinol required for complete reduction of Cu⁺ ⁺ to Cu°is present.

The three phase dispersion is then delivered through stream 44 to asecond settler 46 from which the copper may be recovered and the organicphase 28, which contains solvent, both unused anthraquinol andanthraquinone produced in mixer 42, may be delivered to reaction vessel34. As indicated previously, the Cu⁺ ⁺→Cu⁺ reduction has a rate which isrelatively independent of anthraquinol concentration, and thus, thepartially spent solution of anthraquinol can effect this reductionwithout an additional regeneration.

Since the aqueous raffinate separated in settler 46 will contain asignificant concentration of anthraquinol, prior to its disposal, it maybe delivered through stream 48 to be contacted with an oxidizing agentsuch as air or O₂ in a recovery unit 50. The oxygen oxidizes thedissolved anthraquinol to water insoluble anthraquinone. Theprecipitated anthraquinone may then be removed and recycled to thehydrogenator 40 for further use.

FIG. 3 discloses a schematic diagram of a system which furtherillustrates the two-stage process of the invention. Ammoniacal cupricion containing solution (5 g/l Cu⁺ ⁺) is introduced to first stagereactor (static mixer) 102 through conduit 100 at the rate of 5000gal/min. The pregnant liquor, which may contain 0.05 moles/literchloride or other ions and partially spent 2-ethylanthraquinol receivedfrom the second stage of the process through conduit 104, are intimatelycontacted in reactor 102 and the Cu⁺ ⁺ ions are rapidly reduced to Cu⁺,which are stabilized by the presence of ammonia. The two phase mixtureis then transferred to settler 106 where the organic phase containing2-ethylanthraquinone and trace amounts of its counterpart quinol isseparated from the aqueous phase containing the cuprous amine complexand chloride ion. The organic phase is transferred through conduit 108to the hydrogenator 110 where the quinol is regenerated by hydrogen gasintroduced via conduit 112 at the rate of 1200 CFM. As will beappreciated by those skilled in the art, a suitable hydrogenationcatalyst must be used in hydrogenator 110 and a purge system will benecessary.

The aqueous phase containing cuprous ion is delivered through conduit114 together with a 19 g/l 2-ethylanthraquinol solution, delivered atthe rate of 5000 gal./min. through conduit 116, to second stage reactor(mixer) 118. In reactor 118, the cuprous ion is reduced to copper metalby the excess quinol present and the 3 phase slurry, depleted of solublecopper, is delivered through conduit 120 to 3 phase separator 122.

In separator 122, the partially quinol depleted organic phase isseparated and delivered through conduit 104 to first stage reactor 102.Copper metal is recovered from separator 122 at the rate of 6.25tons/hr. A portion of the copper powder may be recirculated to thesecond stage reactor (mixer) 118 through conduit 134 for seedingpurposes. Seeding technique can be used where it is desirable to obtainthe copper metal in larger particle sizes to produce a higher densitycopper powder. The aqueous phase containing trace quantities ofanthraquinone, significant quantities of anthraquinol, and chloride ionis delivered through conduit 124 to a coalescer 126 where theanthraquinol is oxidized to essentially water insoluble anthraquinone.

The oxidation is accomplished by bubbling air through coalescer 126 fromconduit 128 at the rate of 100 CFM. The copper raffinate is then removedfrom coalescer 126 via conduit 130, the recovered anthraquinone isdelivered to hydrogenator 110 for regeneration via conduit 132. Thecirculating organic phase containing the quinol extractant consists of30% diisobutylketone and 70% xylene.

The recycle of copper powder, after phase separation, back to the mixerhas been found to result in larger particle size and higher density forthe copper powder. This is a rather standard technique called "seeding".Details of a "seeding" experiment appear below.

    ______________________________________                                        SEEDING EXPERIMENT                                                            Aqueous Solution                                                                             Organic Solution                                               ______________________________________                                        10 g/l Cu      25 g/l 2-ethylanthraquinone                                    1 N NH.sub.3   50% 2-ethylhexanol                                             0.25 N NH.sub.4.sup.+                                                                        50% xylenes                                                    ______________________________________                                    

The organic solution was hydrogenated in the presence of a catalyst.

Equal amounts of organic and aqueous solution were then mixed in areactor. After the copper was reduced to copper metal the liquid phaseswere removed from the reactor. The copper powder remained in the reactorand another batch of aqueous and organic were added. Successive runsresulted in the growth of the copper particles.

    ______________________________________                                        COPPER PARTICLE SIZE GROWTH DURING                                            BATCH RECYCLE EXPERIMENT                                                      Per Cent of Particles Greater Than a Given Size                               Cycles                                                                        Volumes  6        13       27     66    88                                    ______________________________________                                         4.2     --       --       --     --    --                                     8.4     100      100      --     --    100                                   16.7     99.4     99.6     100    100   99.8                                  33.5     97.8     99.2     99.4   99.4  99.4                                  67.0     95.6     97.8     98.4   98.4  98.6                                  134      93.2     94.6     96.0   95.6  97.4                                  258      87.2     90.8     91.4   91.4  94.3                                  536      73.0     85.6     86.0   86.0  87.2                                  1,072    42.0     61.4     72.8   65.6  75.2                                  2,145    13.2     21.6     25.8   33.4  37.0                                  4,316     2.6      4.2      4.8    6.2   8.6                                  8,580     0.2      0.6      1.0    0.6   1.4                                  17,157   --        0.2      0.2   --     0.1                                  34,270   --       --       --     --    --                                    ______________________________________                                    

While the above example utilizes 2-ethylanthraquinol as an organicextractant, it will be obvious that other quinolic extractants may beused. Non limiting examples of other useful quinolic compounds include2(lower alkyl)-anthraquinols such as 2-methyl anthraquinol, 2-propylanthraquinol, 2-tert-butyl anthraquinol, 2-isopropyl anthraquinol,2-amyl anthraquinol, etc. While 2(lower alkyl)-anthraquinols arepreferred, it is not necessary to use 2(lower alkyl) anthraquinols.Merely by way of example an anthraquinol of the general formula ##STR5##where, R₁, R₂, R₃, R₄,= H or C₁ H_(x) to C₈ H_(x) can be used toadvantage in the present invention.

A class of anthraquinols known as tetrahydroanthraquinols exists and canbe expected to be present in any system where anthraquinols arehydrogenated.

Tetrahydroanthraquinols have the following structural formula ##STR6##As can be seen from the above formula, tetrahydroanthraquinols differfrom anthraquinols by having four additional hydrogens on one of thearomatic rings. Tetrahydroanthraquinols are slowly built up in theorganic solution by a slow side reaction during the hydrogenation ofanthraquinols. Therefore, they will be present in any commercialprocess. It is possible to suppress the formation reaction and to treata bleed stream to regenerate the anthraquinol from thetetrahydroanthraquinol. However, they have the capability of reducingCu⁺ ⁺ to Cu°. These tetrahydro derivatives are known to be moredifficult to hydrogenate than anthraquinones. In general, the moredifficult a member of the quinone family is to hydrogenate the greaterthe reducing power. Hence tetrahydroderivatives react more rapidly withCu⁺ ⁺ than the anthraquinols. Thus, such derivatives are useable in thepresent process.

In short the present invention can be utilized with any quinoliccompound which is capable of reducing soluble copper and which iscapable of being regenerated back to the quinolic form.

In addition to hydrogen, H₂ S with an amine catalyst can be used toreduce the quinonic compound back to the quinolic compound in thehydrogenation step. Details of this process are set forth in U.S. Pat.No. 3,923,966 to Vaughan, the teachings of which are incorporated hereinby reference.

The invention may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. The presentembodiments are therefore to be considered in all respects asillustrative and not restrictive, the scope of the invention beingindicated by the appended claims rather than by the foregoingdescription, and all changes which come within the meaning and range ofequivalency of the claims are therefore intended to be embraced therein.

I claim:
 1. A process for producing metallic copper from an aqueouscopper solution, said process being characterized by the steps ofcontacting said aqueous solution with a quinolic compound to precipitatemetallic copper, said quinolic compound being dissolved in asubstantially water immiscible solvent capable of also dissolving thequinonic compound which forms during the reactions, and separatingmetallic copper from the reaction system, wherein the improvementcomprises:(a) oxidizing the water solubilized unreacted quinoliccompound which becomes dissolved in the aqueous solution after theprecipitation of copper metal to form a water insoluble quinoniccompound; (b) recovering the quinonic compound produced in step (a); and(c) reducing the quinonic compound produced in step (b) to the quinoniccompound for reuse in the water immiscible solvent.
 2. The process asset forth in claim 1 wherein said oxidizing step (a) is effected afterseparating the aqueous solution containing a dissolved quinolic compoundfrom said water immiscible solvent.
 3. The process as set forth in claim2 wherein said oxidizing step (a) is effected by contacting said aqueoussolution with an oxidizing gas.
 4. The process as set forth in claim 3wherein said oxidizing gas comprises oxygen.
 5. The process as set forthin claim 1 wherein step (c) is effected by reacting said quinoniccompound with hydrogen in the presence of a hydrogenation catalyst. 6.The process as set forth in claim 1 wherein said copper containingsolution comprises an ammoniacal cupric solution having a pH of about10.
 7. The process as set forth in claim 1 wherein said substantiallywater immiscible solvent comprises a mixture of an organic nonpolarsolvent and an organic polar solvent and wherein said mixture comprisesmore than 50% by weight of said nonpolar solvent.
 8. The process as setforth in claim 7 wherein said nonpolar solvent is selected from thegroup consisting of xylene, toluene, other lower alkyl-substitutedbenzenes, and naphthalenes, and said polar solvent is selected from thegroup consisting of alcohols, ketones, and esters.
 9. The process as setforth in claim 1 wherein said quinolic compound is selected from thegroup consisting of 2-methyl-anthraquinol, 2-ethyl-anthraquinol,2-propyl-anthraquinol, 2-tert-butyl-anthraquinol,2-isopropyl-anthraquinol, and 2-amyl-anthraquinol.
 10. A process forproducing copper metal from an aqueous ammoniacal cupric ion containingsolution, said process being characterized by the steps of:(1) mixing astoichiometric excess of quinolic compound and an aqueous ammoniacalsolution of cuprous ions in a first reactor to precipitate copper metaland to oxidize part of said quinolic compound to a quinonic compound,the remaining quinolic compound and the produced quinonic compound beingdissolved in a substantially water immiscible solvent; (2) separatingthe water immiscible solvent, the copper metal and the aqueous solution;(3) oxidizing water solubilized quinolic compound which becomesdissolved in the aqueous solution after the precipitation of coppermetal in step (1) to form a water insoluble quinonic compound; (4)recovering the quinonic compound produced in step (3); (5) reducing thequinonic compound produced in step (4) to the quinolic compound forreuse in the water immiscible solvent of step (1). (6) mixing theimmiscible solvent containing a portion of the remaining quinoliccompound which is separated in step (2) with an ammoniacal solution ofcupric ions in a second reactor to enable said quinolic compound toreduce said cupric ions to cuprous ions and to produce further quinoniccompound; (7) separating the immiscible solvent from the solution ofcuprous ions produced in step (6) and reducing the quinonic compound inthe immiscible solvent for reuse in step (6); and (8) adding thesolution of cuprous ions separated in step (7) to said first reactor andrepeating step (1).
 11. The process as set forth in claim 10 whereinsaid oxidizing step (3) is effected by contacting said aqueous solutionwith an oxidizing gas.
 12. The process as set forth in claim 11 whereinsaid oxidizing gas comprises oxygen.
 13. The process as set forth inclaim 11 wherein the reduction of steps (5) and (7) is effected byreacting the quinonic compound with hydrogen in the presence of ahydrogenation catalyst.
 14. The process as set forth in claim 11 whereinthe reduction of steps (5) and (7) is effected by reacting said quinoniccompound with H₂ S in the presence of an amine catalyst.
 15. A processfor producing copper metal from an aqueous ammoniacal cupric ioncontaining solution, said process being characterized by the stepsof:(1) mixing a stoichiometric excess of quinolic compound and anaqueous ammoniacal solution of cuprous ions in a first reactor toprecipitate copper metal and to oxidize part of said quinolic compoundto a quinonic compound, said ammoniacal solution also containing ionsselected from the group consisting of chloride ions, bromide ions,thiocyanate ions and mixtures thereof in amounts effective to increasethe rate of copper precipitation, the starting quinolic compound and theproduced quinonic compound being dissolved in a substantially waterimmiscible solvent; (2) separating the water immiscible solvent, thecopper metal and the aqueous solution; (3) oxidizing water solubilizedquinolic compound which becomes dissolved in the aqueous solution afterthe precipitation of copper metal in step (1) to form a water insolublequinonic compound; (4) recovering the quinonic compound produced in step(3);
 5. reducing the quinonic compound produced in step (4) to thequinolic compound for reuse in the water immiscible solvent of step (1);(6) mixing the immiscible solvent containing a portion of the remainingquinolic compound which is separated in step (2) with an ammoniacalsolution of cupric ions in a second reactor to enable said quinoliccompound to reduce said cupric ions to cuprous ions and to producefurther quinonic compound; (7) separating the immiscible solvent fromthe solution of cuprous ions produced in step (6) and reducing thequinonic compound in the immiscible solvent for reuse in step (6); and(8) adding the solution of cuprous ions separated in step (7) to saidfirst reactor and repeating step (1).
 16. The process as set forth inclaim 15 wherein said oxidizing step (3) is effected by contacting saidaqueous solution with an oxidizing gas.
 17. The process as set forth inclaim 16 wherein said oxidizing gas comprises oxygen.
 18. The process asset forth in claim 16 wherein the reduction of steps (5) and (7) iseffected by reacting the quinonic compound with hydrogen in the presenceof a hydrogenation catalyst.
 19. The process as set forth in claim 16wherein the reduction of step (5) and (7) is effected by reacting saidquinonic compound with H₂ S in the presence of an amine catalyst. 20.The process as set forth in claim 15 wherein said ammoniacal solutioncontains chloride ions in a concentration between the range of 0.1M and0.0001M.
 21. The process as set forth in claim 20 wherein the ratio ofchloride concentration to copper concentration is between about 1 and0.01.
 22. The process as set forth in claim 21 wherein the pH of saidsolution is about
 10. 23. The process as set forth in claim 22 whereinsaid substantially water immiscible solvent comprises a mixture of anorganic nonpolar solvent and an organic polar solvent, and wherein saidmixture comprises more than 50% by weight of said nonpolar solvent. 24.The process as set forth in claim 23 wherein said nonpolar solvent isselected from the group consisting of xylene, toluene, other loweralkyl-substituted benzenes, and naphthalenes, and said polar solvent isselected from the group consisting of alcohols, ketones, and esters. 25.The process as set forth in claim 24 wherein said quinolic compound isselected from the group consisting of 2-methyl anthraquinol,2-ethyl-anthraquinol, 2-propyl-anthraquinol, 2-tert-butyl-anthraquinol,2-isopropyl-anthraquinol, and 2-amyl-anthraquinol.